Project Summary/Abstract The Research Plan describes a series of experiments that will examine how spatial information is processed in the mammalian brain. Previous studies have identified a population of cells that are tuned to a subject?s directional heading These so-called head direction cells are thought to underlie one?s sense of direction. The neural basis for this computation is believed to reside in an attractor network at subcortical levels. Further, this network is believed to integrate information about self-motion and visual landmarks to yield an internal model of one?s sense of orientation. To understand how this integration is accomplished, it is crucial to know what information is encoded by inputs into the head direction system. This system ultimately guides one?s navigational behavior. This Brain Initiative proposal contains three aims that collectively will uncover a detailed understanding of how the head direction signal is constructed and used to guide behavior. Specifically, Aim 1 will identify the specific self- motion information to the head direction system and determine whether those inputs are sufficient to update the head direction signal. The vast majority of head direction cell studies have been conduted in rodents. Aim 2 will seek to identify head direction cells in non-human primates and systematically dissociate the contributions of eye, head, and body direction to the head direction signal. The first two aims focus on understanding how self-motion signals are integrated at subcortical nuclei that are believed to generate the head direction signal. But it is well-known that the head direction system must combine visual landmark information that is derived in the cortex. Thus, Aim 3 will use calcium-imaging techniques in retrosplenial cortex to reveal how conflicts between visual landmarks and self-motion cues are resolved. All aims will test quantitative predictions from head direction circuit models and based on findings in the three aims will derive new and more detailed networks that account for how the signal is generated at the neuronal level. Five investigators from two institutions will combine their expertise in high density ensemble recording, calcium imaging, and modeling/data analysis in behaving animals to understand in detail how the brain implements a neural compass.